title: Morphine biosynthesis in opium poppy involves two cell types: sieve elements and laticifers.
abstract: Immunofluorescence labeling and shotgun proteomics were used to establish the cell type-specific localization of morphine biosynthesis in opium poppy (Papaver somniferum). Polyclonal antibodies for each of six enzymes involved in converting (R)-reticuline to morphine detected corresponding antigens in sieve elements of the phloem, as described previously for all upstream enzymes transforming (S)-norcoclaurine to (S)-reticuline. Validated shotgun proteomics performed on whole-stem and latex total protein extracts generated 2031 and 830 distinct protein families, respectively. Proteins corresponding to nine morphine biosynthetic enzymes were represented in the whole stem, whereas only four of the final five pathway enzymes were detected in the latex. Salutaridine synthase was detected in the whole stem, but not in the latex subproteome. The final three enzymes converting thebaine to morphine were among the most abundant active latex proteins despite a limited occurrence in laticifers suggested by immunofluorescence labeling. Multiple charge isoforms of two key O-demethylases in the latex were revealed by two-dimensional immunoblot analysis. Salutaridine biosynthesis appears to occur only in sieve elements, whereas conversion of thebaine to morphine is predominant in adjacent laticifers, which contain morphine-rich latex. Complementary use of immunofluorescence labeling and shotgun proteomics has substantially resolved the cellular localization of morphine biosynthesis in opium poppy.
authors.affiliation: Department of Biological Sciences, University of Calgary, Calgary, Alberta T2N 1N4, Canada.
authors.forename: Akpevwe
authors.initials: A
authors.lastname: Onoyovwe
authors.forename: Jillian M
authors.initials: JM
authors.lastname: Hagel
authors.forename: Xue
authors.initials: X
authors.lastname: Chen
authors.forename: Morgan F
authors.initials: MF
authors.lastname: Khan
authors.forename: David C
authors.initials: DC
authors.lastname: Schriemer
authors.forename: Peter J
authors.initials: PJ
authors.lastname: Facchini
mesh_terms: D000470:Alkaloids / Q000378:metabolism; D007527:Isoenzymes / Q000378:metabolism; D008969:Molecular Sequence Data; D009019:Morphinans / Q000378:metabolism; D009020:Morphine / Q000096:biosynthesis*; D010207:Papaver / Q000166:cytology* / Q000378:metabolism; D059828:Plant Cells / Q000201:enzymology*; D010940:Plant Proteins / Q000378:metabolism*; D040901:Proteomics; D044005:Tetrahydroisoquinolines / Q000378:metabolism; D013797:Thebaine / Q000378:metabolism
chemical_list: D000470:Alkaloids; D007527:Isoenzymes; D009019:Morphinans; D010940:Plant Proteins; D044005:Tetrahydroisoquinolines; D013797:Thebaine; D009020:Morphine; C009270:salutaridine; C012348:higenamine